Effect of pH on the aluminum salts hydrolysis during coagulation process: Formation and decomposition of polymeric aluminum species
Effect of pH on the aluminum salts hydrolysis during coagulation process: Formation and decomposition of polymeric aluminum species
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DOI：
10.1016/j.jcis.2008.10.020
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发表时间：
2009-02-01
影响因子：
9.9
通讯作者：
Qu, Jiuhui
中科院分区：
文献类型：
--
作者：
Zhao, He;Liu, Huijuan;Qu, Jiuhui
采用电喷雾电离(ESI)质谱仪，详细研究了pH对低浓度三氯化铝水解反应的影响。特别讨论了聚合铝物种的形成和分解过程。当凝固剂AlCl3稀释到正常凝固剂剂量(1.5×10~(-4)摩尔/L)时，立即发生水解。在pH值为4.0时，主要产物为单体铝和二聚铝。随着pH值的升高，水解和聚合过程加快。单体和二聚铝物种在pH为4.8时被水解和聚合成小的聚合铝物种(Al-3-Al-5物种)。在pH值为5.0时，通过聚集和自组装，小分子聚合铝物种聚合成中等聚合物种(Al-6-Al-10物种)。同样，小的和中等的聚合铝物种进一步聚集成大的聚合物种(Al-11-Al-21物种)。当pH值达到5.8时，亚稳态的中大分子物种分解成小的铝物种，然后进一步分解成二聚体物种。当pH升高到6.4时，大部分铝物种形成Al(OH)(3)无定形絮体。据此，提出了混凝剂从聚合到分解的水解机理。聚合铝物种在AlCl3溶液中的形成和分解遵循“核-键”模型，而Keggin-Al-13物种在聚铝溶液中的形成和分解符合“笼状”模型。(C)2008 Elsevier Inc.保留所有权利。
Effect of pH on the aluminum chloride hydrolysis at low concentration was investigated in detail by electrospray ionization (ESI) mass spectrometry. In particular, formation and decomposition processes of polymeric aluminum species were discussed. When Coagulant AlCl3 was diluted to normal coagulant dose (1.5 x 10(-4) mol/L), hydrolysis occurred immediately. Monomeric and dimeric aluminum species were the main products at pH 4.0. With pH increasing, hydrolysis and polymerization processes were accelerated. Monomeric and dimeric aluminum species hydrolyzed and polymerized into small polymeric aluminum species (Al-3-Al-5 species) at pH 4.8. Through aggregation and self-assembly, the small polymeric aluminum species polymerized into median polymeric species (Al-6-Al-10 species) at pH 5.0. In the same way, small and median polymeric aluminum species further aggregated into large polymeric species (Al-11-Al-21 species). When pH was up to 5.8, metastable median and large polymers species decomposed into small aluminum species, then further disaggregated into dimeric species. With pH increased to 6.4, majority of aluminum species formed to Al(OH)(3) amorphous flocs. Accordingly, coagulant hydrolysis mechanism from polymerization toward decomposition was proposed. Furthermore, formation and decomposition of polymeric aluminum species in AlCl3 solution followed the "Core-links" model, while those of Keggin-Al-13 species in polyaluminum solution was based on the "Cage-like" model. (C) 2008 Elsevier Inc. All rights reserved.